This invention relates to electrical indicators.
The present invention is concerned especially with electrical indicators of a kind in which an analogue representation in accordance with the value of an input variable is provided by selective brightening along a reference scale (whether calibrated or otherwise) of a series of electrically-energizable light-emitting elements.
Electrical indicators of this latter kind (referred to herein as "of the kind specified") have already been proposed, and in this respect it has been proposed to arrange that only one of the elements is selected for energization at any time, so that brightening occurs at only one point along the scale. The selection of the particular element energized, and thereby of the location along the scale of the brightening, is in this case made in accordance with the value of the input variable such that the displacement of the brightening point from the scale zero or other datum provides a measure of that value. The indication provided is therefore analogous to that provided by a conventional mechanical-pointer instrument, but with the `reading` against the scale signified in this case by the bright, energized element rather than by the pointer. Although such an indication may be entirely satisfactory, there are circumstances in which it may be indistinct. These circumstances arise especially where significant accuracy of indication is required against the scale since the width of each element, and therefore its visual distinguishability when energized, is then necessarily limited.
The problem of ensuring adequate visual distinguishability can be overcome by arranging that instead of energizing just the one element, all the other elements of the series up to that element are energized also. The indication provided under this mode of operation is comparable with that provided by a conventional thermometer, the `reading` in this case being taken by reference to the location against the scale of the readily distinguishable interface between the energized, bright elements and the unenergized, dark elements. However, a very substantial increase in electrical-power dissipation in the indicator is in general required for this mode of operation, and this can present an electrical-supply or operating-temperature problem, or both. Such problems become especially relevant where a large number of indicators are required to be operated together.